I'd say, first of all choose a solution that your team is comfortable with. If you are more windows guy, go for Windows 2016 boxes, if you are a linux shop, go for Linux servers, any major distribution is ok. My personal opinion, unless you know it really well, avoid less known distributions; not because they are not supported, but our support will probably have more experience with major ones.
Then,anything works, my choice would go for servers with local internal storage, but there's no real preference, other than using a solution (again, not mandatory, just a best practice from my experience) where the Veeam datamover can be deployed locally, it makes the design more simple as you can easily predict the data streams that will happen. Once the solution starts to scale (and with Cloud Connect, it CAN happen) the more simple the design is, the better.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1